WASHINGTON (AP) -- A Russian fighter jet made multiple, close-range passes near an American warship in the Black Sea for more than 90 minutes Saturday amid escalating tensions in the region, U.S. military officials said Monday.

In the first public account of the incident, the officials said the Russian Fencer made 12 passes, and flew within 1,000 yards of the USS Donald Cook, a Navy destroyer, at about 500 feet above sea level.

The U.S. warship issued several radio queries and warnings using international emergency circuits, but the Russian aircraft did not respond.

"This provocative and unprofessional Russian action is inconsistent with international protocols and previous agreements on the professional interaction between our militaries," said Army Col. Steve Warren, a Pentagon spokesman.

The fighter appeared to be unarmed and never was in danger of coming in contact with the ship, said the officials. The passes, which occurred in the early evening there, ended without incident. A second Russian fighter jet flew at a higher altitude and was not a concern, said Warren.

A U.S. military official also said that a Russian Navy ship, a frigate, has been shadowing the U.S. warship, remaining within visual distance but not close enough to be unsafe. The official was not authorized to discuss the incident publicly so spoke on condition of anonymity.

Warren said that he is not aware of any official communication or protests by the U.S. to the Russians about incident.

The USS Donald Cook has been conducting routine operations in international waters east of Romania. The ship, which carries helicopters, was deployed to the Black Sea on April 10, in the wake of the Russian military takeover of Ukraine's Crimea region and ongoing unrest there. U.S. military officials have said the deployment is part of an effort to reassure allies and partners in the region.

Ukraine's acting President Oleksandr Turchynov on Monday called for the deployment of United Nations peacekeeping troops in the east of the country, where pro-Russian insurgents have occupied buildings in nearly 10 cities. The gunmen are demanding more autonomy from the central government and closer ties with Russia.

The West has accused Moscow of fomenting the unrest. And European Union foreign ministers are meeting in Luxembourg Monday to consider additional sanctions against Russian officials because of Moscow's annexation of Crimea.

The USS Donald Cook is now in port at Constanta, Romania.

Romanian President Traian Basescu visited the ship Monday and said a second U.S. Navy warship - a frigate from the Navy's Sixth Fleet in the Mediterranean Sea - is also heading to the Black Sea.

"My visit to the ship is symbolic, which first of all shows our respect to our NATO allies' reaction who have strengthened their presence in the Black Sea after Russia's annexation of Crimea," said Basescu, who is a former ship captain. He said the Russians "had created a circle of fire around the Black Sea."

The U.S. frigate, which has not yet been identified, is expected to arrive in the Black Sea in the next two weeks. According to a U.S. military official, the frigate is likely to replace the USS Donald Cook, which is expected to return to the Mediterranean Sea.

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Time to re-think the “re-balancing” to the Asia-Pacific region? Since the end of the Cold War the United States has markedly reduced America forces, including those of the United States Navy (USN), based in Europe in support of the North Atlantic Treaty Organization (NATO). In the last few years much attention has been given to the so-called ‘pivot’ or “re-balancing” of America’s global military posture toward the Asia-Pacific region. This is especially the case for the forward power projection capabilities of the USN. Although NATO’s focus has always been on land and land-based air power, maritime forces have long been an important part of the Alliance’s collective military posture. This has been so on the ‘high seas’ and most notably in the littoral waters surrounding the European mainland. The events in Ukraine, and the close shadowing of an American warship by a Russian fighter in the Black Sea, are a reminder that American sea power still has a role to play in securing U.S. interests in Europe and in providing substantive and above all symbolic assurance to NATO allies, particularly the newer allies on the Alliance’s eastern perimeter. Thus, while a shifting of emphasis westward is warranted given its rising strategic and economic importance to the United States, it may not be wise for Washington to re-balance America’s still dominant naval forces too far in favor of the Asia-Pacific region.